1. Field of the Invention
The present invention relates to a printed circuit board (PCB) assembly, and particularly to a supporting tray used during wave soldering of electronic components onto a PCB.
2. Description of the Prior Art
Wave soldering generally comprises three steps. First, a fluxer applies flux to a bottom side of a PCB to clean and prepare solder pad surfaces thereof, so that solder can properly adhere to the solder pad surfaces. Then the PCB is preheated. Finally, the PCB is received in a supporting tray, which is then placed in a wave solder machine. The supporting tray with the PCB is moved across a solder wave in the wave solder machine, thereby electrically connecting leads of various electronic devices to the solder pads of the PCB. Different types of PCBs exhibit various different characteristics during wave soldering, because of different distributions of electronic components thereon. Adjusting parameters of the wave solder machine itself can generally bring about only a 15% improvement in soldering efficacy. Conventionally, the efficacy of soldering is improved by adjusting an angle of the PCB with respect to a direction of flow of the solder waves in the wave solder machine.
A conventional supporting tray is shown in FIG. 3. The supporting tray comprises a base 20′, a receiving portion 22′ defined in the base 20′, and a plurality of retaining clasps 21′ provided around the receiving portion 22′. In use, a PCB 10′ is received in the receiving portion 22′. The retaining clasps 21′ are rotated to retain the PCB 10′ in the receiving portion 22′. An angle of the PCB 10′ with respect to a direction of flow of the solder waves is fixed according to an angle of the receiving portion 22′ relative to the base 20′. Generally, said angle of the receiving portion 22′ is determined according to past experience with wave soldering of other identical PCBs 10′, to provide optimal soldering quality. However, if it is desired to wave solder another type of PCB, said angle of the receiving portion 22′ may not yield optimal soldering quality because of the different distribution of electronic components on the other type of PCB. In such case, said angle of the receiving portion 22′ cannot be adjusted, and a new supporting tray having a differently oriented receiving portion must be obtained and tried. If this new supporting tray also fails to yield optimal soldering quality, still another new supporting tray must be obtained and tried, and so on until a new supporting tray yielding optimal soldering quality is finally obtained. This problem may be even further multiplied when it is desired to wave solder yet another type of PCB. The need to provide a plurality of supporting trays, many of which may ultimately prove to be redundant, is time-consuming, wasteful and costly.
Thus, a single supporting tray which overcomes the above-mentioned problems is desired.